<html>
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>学习jQuery对象属性等</title>
</head>
<body>
    <u1>
        <li id="elem">第一个节点</li>
        <li>第二个节点</li>
        <li>第三个节点</li>
        <li>第四个节点</li>
    </u1>
</body>
<script src="./js/jQuery.js"></script>
<script>

    console.log( $("#elem") );
    console.log( $("#elem").length );

    console.log( $("u1 li") );
    console.log( $("u1 li").length );
    
    console.log( $("#elem2") );
    console.log( $("#elem2").length );
    
</script>
</html